Climate shapes the spatial pattern in local β-diversity of alpine grasslands on the Tibetan Plateau.

Little is known about the structure of plant communities across the vast Tibetan Plateau, which supports at least 12,000 species of alpine vascular plants including over 2000 endemics. We recorded species abundance in 485 sites stretching across 6000 km of the plateau. At each site, species abundance was measured in three quadrats that were 40 m apart, allowing us to quantify local β-diversity within the site. We found that local β-diversity in alpine meadows and steppes was significantly higher than expected by chance, indicating intraspecific aggregation within the sites. After controlling for random sampling effects, the magnitude of local β-diversity varied across the plateau: there was a positive relationship from west to east corresponding to increased rainfall; there were hump-shaped relationships with elevation and latitude. These patterns were driven mainly by regional variation in climate, but also by local soil properties and grazing regimes (our structural equation models (SEMs) explained 27 % and 26 % of variation in alpine meadows and steppes, respectively). Unexpectedly, precipitation-related variables were the strongest predictors in cold-wet alpine meadows while temperature-related variables were the strongest predictors in dry-warm alpine steppes. Our findings support the hypothesis that environmental filtering is largely responsible for local β-diversity of alpine grasslands across the Tibetan Plateau. We discuss how these findings inform efforts to conserve fragile alpine ecosystems threatened by rapid climate warming and overgrazing.